This invention relates to a clamp for clamping a workpiece, and is particularly, although not exclusively, concerned with a clamp for clamping an aerofoiled component for machining purposes.
The secure clamping of aerofoiled components presents difficulties because the aerofoil sections do not have flat, parallel surfaces. Also, aerofoil components formed by forging have dimensional and shape differences from one another which means that a clamping structure shaped to fit perfectly with one component will not fit perfectly with another. Such imperfect fits can result in inadequate clamping and/or marking of the aerofoil surface.
A forged aerofoil component, for example a compressor rotor blade of a gas turbine engine, must undergo various operations after forging in order to remove forging flash and forging locating pips, to form blade edge and root profiles and to tip the blade to the required length. To perform these operations, the component must be held securely while exposing those parts on which the operations are to be performed. Hand polishing, followed by a vibro-polishing operation, is commonly used to form the desired circular profiles of blade chordal edges, but this often results in the chordal edges having flats or facets which, while within engineering tolerances, do not provide optimum aerodynamic performance, resulting in a loss of efficiency of the compressor module. It is thus desirable for the aerofoil finishing operations to be performed by machine, which requires secure fixing of the component while the machining and polishing operations are performed.
An object of the present invention is to provide a clamp which is able to support a workpiece having variable profiles and dimensions.
A further object of the present invention is to provide a clamp with a workpiece clamping element which is pivotable to adapt to the surface profile of a clamped workpiece.
A yet further object of the present invention is to provide a clamp which provides firm support to parts of a component during the performance of machining and polishing operations.
According to the present invention there is provided a clamp for clamping a workpiece, the clamp comprising:
a support body;
a workpiece supporting element mounted on the support body:
a clamping member mounted on the support body for displacement towards and away from the support body;
a workpiece clamping element mounted on the clamping member;
securing means adapted to retain the clamping member in a clamping position in which, in use, the workpiece clamping element applies a clamping force to a workpiece clamped between the workpiece clamping element and the workpiece supporting element; and
connecting means which connects the workpiece clamping element to the clamping member for pivoting displacement relatively to the clamping member about axes lying in a plane extending transversely of the line of action of the clamping force, and for linear movement relatively to the clamping member in a direction substantially transverse to the line of action of the clamping force, whereby the workpiece clamping element is self-aligning with the surface of a clamped workpiece.
Because the workpiece clamping element is self-aligning, it is able to adapt to variations in surface profile and dimensions of the clamped workpiece, for example a forged aerofoil component.
The pivoting displacement of the workpiece clamping element may be limited, for example by contact between the workpiece clamping element and the clamping member.
In one embodiment in accordance with the present invention, the pivoting displacement is achieved by means of a ball and socket connection. The ball and socket connection may comprise a part-spherical ball element mounted on the clamping member, which engages a socket formed in the workpiece clamping element. Separate means, for example a transverse pin, may be provided to retain the workpiece clamping element on the clamping member.
Resilient means may be provided for biasing the workpiece clamping element into engagement with a face of the workpiece, the biasing force extending transversely of the line of action of the clamping force.
In an alternative embodiment, the pivoting displacement of the workpiece clamping element may be provided by connecting the workpiece clamping element to the clamping member by means of a resilient connecting element. This connecting element may comprise a necked region between the clamping member and the workpiece clamping element, the clamping member, the necked region and the workpiece clamping element then being integral with each other. The connecting element may be situated generally centrally of the workpiece clamping element.
Around the connecting element, the workpiece clamping element may be separated from the clamping member by machined slots, closure of the slots upon deflection of the workpiece clamping element limiting the extent of displacement of the workpiece clamping element relatively to the clamping member.
The clamp may include at least one locating element, spaced from the workpiece supporting element and the workpiece clamping element, for engagement with a surface profile of the workpiece to locate the workpiece within the clamp. The locating element may comprise a recess for receiving a protrusion or pip on the workpiece.
The support body may be mounted on a fixture for removable fitting to a machine tool or other workpiece processing equipment.